Function memory_bound_workers 

pub fn memory_bound_workers() -> usize

Workers worth using for memory-bound kernels (copies, byte swaps, packed unpack, lookup curves). Measured on a 16-thread x86 server: such loops peak at ~4 threads and get 1.7-1.9x slower at 16 from memory-controller and page-fault contention. Machines with more bandwidth per core scale further, so the cap grows with the thread count.